Text of Hosea 9.9
"Gibeah" or "the days of Gibeah" are a recurring theme in the book of Hosea, being mentioned in Hosea 5.8 (LEB)
Blow the horn in Gibeah, the trumpet in Ramah. Sound the alarm in Beth-aven; look behind you, Benjamin.
in Hosea 9.9 (LEB):
They deeply corrupted themselves as in the days of Gibeah; he will remember their sin, he will punish their sins.
and finally in Hosea 10.9-11 (LEB):
From the days of Gibeah you have sinned, O Israel; there they have remained. Will not war in Gibeah overtake them against the children of evil? In my desire I will punish them; nations will be gathered against them when they are punished for their double iniquities.
MT (Hosea 10.9-11):
מִימֵי֙ הַגִּבְעָ֔ה חָטָ֖אתָ יִשְׂרָאֵ֑ל שָׁ֣ם עָמָ֔דוּ לֹֽא־תַשִּׂיגֵ֧ם בַּגִּבְעָ֛ה מִלְחָמָ֖ה עַל־בְּנֵ֥י עַֽלְוָֽה׃
בְּאַוָּתִ֖י וְאֶסֳּרֵ֑ם וְאֻסְּפ֤וּ עֲלֵיהֶם֙ עַמִּ֔ים בְּאָסְרָ֖ם לִשְׁתֵּ֥י עֵינֹתָם׃
וְאֶפְרַ֜יִם עֶגְלָ֤ה מְלֻמָּדָה֙ אֹהַ֣בְתִּי לָד֔וּשׁ וַאֲנִ֣י עָבַ֔רְתִּי עַל־ט֖וּב צַוָּארָ֑הּ אַרְכִּ֤יב אֶפְרַ֙יִם֙ יַחֲר֣וֹשׁ יְהוּדָ֔ה יְשַׂדֶּד־ל֖וֹ יַעֲקֹֽב׃
and LXX (LES):
From the time the hills [gibeah = 'hill'] stood there, Israel has sinned. A war upon the children of injustice, has it not seized them on the hill [verse 10] to chastise them? And peoples will gather against them, when they chastise them for their two offenses.
What is the referent for "Days of Gibeah"?
The question is about the referent "days of Gibeah" in Hosea 10.9. There are (as I see it) four candidates for events that happened in Gibeah:
Joshua 10.1-28. At Gilgal, Joshua made peace with men from Gibeon who cunningly tricked him and afterwards war came when the surrounding tribes attacked, and Joshua marched through the night to Gibeon and attacked the attackers. Stones fell from heaven to destroy them, the sun and moon stopped above Gibeah, and the five kings were hanged on trees until evening, then placed in a cave with a stone against it.
Judges 19-21. The Levite rides up at night to Gibeah, men surround the house where he shelters, his concubine is killed, leading to war where the other tribes attack Gibeon, reducing Benjamin to 600 men hiding on the rock of Rimmon.
1 Sam 10-11. Saul is at his home in Gibeah when the messengers arrive of the threats against the city of Jabesh-Gilead. Like the Levite's concubine, Saul cuts up two oxen, sends them out, and then wages war to relieve the city.
"Days of Gibeah" could refer to the kingship of Saul as a whole.
So the question is which of the above four (or perhaps a completely different) event is being referenced in Hosea 10.9?
To help answer that question also requires parsing the second half of the verse, which has different readings in the LXX and the MT.
Rabbinical commentary seems to focus on the kingship of Saul as "the days of Gibeah". Here is the Targum Onkelos:
From the days of Gibeah the people of the house of Israel have sinned. There they arose and rebelled against my Memra, by appointing a king over them, but they were not worthy that the kingship should be established for them in Gibeah. There warriors came against them for slaughter; fathers with sons went up
Modern academic commentaries, however, tend to focus on the Levite and his concubine. Here is Hermeneia:
Now he not only says: “As in the days of Gibeah,” but “since the days of Gibeah you have sinned. There they have remained.” In v 9* עמד means “to persist in the same attitude,” “remain unchanged.” It is the opposite concept of “return,” which Hosea has long since called for.15 Thus for Hosea history was of utmost importance because past historical events are typical for and determinative of the present time. There is even less reason here than in 9:9* to consider this a reference to the beginning of the monarchy. Gibeah was certainly Saul’s royal residence,15a but it was not the place of Israel’s guilt in connection with the inception of the monarchy. On the other hand, Hosea’s words become understandable in the light of Benjamin’s terrible offense against the sojourning Levite—a shocking transgression against divine law in Israel (Ju 19:30*)—together with the destructive war of retribution that followed (Ju 20:34*, 48*). Since Gibeah’s former guilt is also its present guilt, the city’s former disaster will come once again to Gibeah, despite the mockery the prophet’s enemies make of him.17 The בני עלוה are the rebellious agitators. The word עלוה, like עולתה denotes the “perversity” and “baseness” seen in apostasy (Ezek 28:15f*) and hostility (Ps 89:23*; 2 Sam 7:10*); as revolt against the legitimate sovereign, it was a capital offense (2 Sam 3:34*). Thus Yahweh’s judgment comes upon present Israel as the “people of Gibeah”; similarly Isaiah called Jerusalem “people of Gomorrah” and her leaders “rulers of Sodom” (Is 1:10*).
Likewise we have the Word Biblical Commentary:
The “days of Gibeah” again constitute a paradigm of the depth to which Israel is capable of sinking morally and religiously, as in 9:9 (cf. Isa 1:10). “There they have stayed” (שם עמדו) provides a link with the third sentence of the verse. Israel—the whole nation—is still at Gibeah (Judg 19) so war (Judg 20) will soon overtake them at Gibeah, i.e., still in their sins. It is also possible that the imperfect verb תשיגם is to be construed in the past tense (so Andersen and Freedman, 560, 565; cf. n. 9.d), i.e., “Did not war overtake them in Gibeah …?” The point then would be: “If God punished Israel by war that time, will he not do it again?”
And the NICOT commentary:
His reference is probably related to the sexual horror and resulting warfare in Judg. 19–21, but his allusions are difficult to correlate with the account in Judges. Hosea may well have had different source material upon which to draw than now contained in the other biblical account.
 Cathcart, K. J., McNamara, M., & Maher, M. (1990). Editors’ Foreword. In K. J. Cathcart, M. Maher, & M. McNamara (Eds.), K. J. Cathcart & R. P. Gordon (Trans.), The Aramaic Bible: The Targum of the Minor Prophets (Vol. 14, Ho 10:9). Collegeville, MN: The Liturgical Press.
 Wolff, H. W. (1974). Hosea: a commentary on the book of the Prophet Hosea (p. 184). Philadelphia: Fortress Press.
 Stuart, D. (1987). Hosea–Jonah (Vol. 31, p. 168). Dallas: Word, Incorporated.
 Dearman, J. A. (2010). The Book of Hosea (p. 268). Grand Rapids, MI; Cambridge, U.K.: William B. Eerdmans Publishing Company.